Typical printers and copiers used for producing printed copies of material on sheets of paper are known to cause various amounts of curling in the process created by the application of ink and heat in the reproduction process. The extent of the curl transverse to the direction of movement of the sheets of paper through and from the printing and copying machine varies considerably. Different paper thicknesses react and are curled somewhat differently. Different paper weights and content of the paper, as well as remanufactured paper, all exhibit different degrees of the tendency to curl, depending upon the applied heat, the surface area covered by the printed material, the moisture content in the paper and other factors.
In order to avoid, as much as possible, the tendency of the paper to curl during the printing or copying process so as to enable post-processing of the finished sheets by receiving the sheets in order and in reasonably well defined stacks or sets, without interference from excessive curl in the paper, various devices have been developed for decurling the paper as it exits the reproduction machine, including devices which tend to press the paper, devices for corrugating the sheets by application of deforming pressure laterally of the direction of sheet feed so as to add beam strength to the sheets of paper, and various other devices have been developed for the purpose of reversely deforming the sheets so as to eliminate the curl as the paper exits the reproducing machine and enters receivers, stackers, sorters or other sheet post-processing devices.
Included in the prior art devices for laterally or transversely deforming the sheets as they exit the reproduction apparatus is, for example, Coombs U.S. Pat. No. 5,066,984, granted Nov. 19, 1991. This patent discloses a decurling device which is disposed in the path of paper sheets leaving a printing unit or processor, such as an office copier or printer, and has an arcuate concave guide and a roll spaced from the guide to form a sheet path which is curved or arched oppositely to the direction in which the sheet is curled in the processor. The space between the guide and the roller is greater than the thickness of the paper and the paper is bent in the direction opposite to its curl as it passes through the arched space, while the beam strength of the paper and the change in direction of the paper maintain adequate drive friction on the sheet to feed the sheet. A selector isolates the decurler when it is not needed.
A variation of the device shown in the Coombs '984 patent is shown in Leemhuis et al U.S. Pat. No. 5,316,539, granted May 31, 1994, wherein the arched decurling guide is pivoted and biased by a spring towards the decurling roller which defines with the guide the gap or space in proportion to the rigidity or beam strength of the paper to be decurled so as to provide automatic adjustment based on papers within a range of different rigidity or beam strength.